1. Field of the Invention
The present invention relates to a method and a device using pyrolysis for recycling used printed circuit board, and more particularly, to a method and a device using pyrolysis for recycling used printed circuit board which can greatly enhance the safety of the pyrolysis process, improve the reusability of the pyrolysis gas, strengthen the stability of the processing device, ensure the safety of the operator and reduce the cost.
2. Description of the Prior Art
The inventor of this invention has disclosed the Taiwan Patent Application No. 095102342 titled “The method for recycling used printed circuit board” in Jan. 20th, 2006 and been awarded Taiwan Patent No.I268184 for the same case, which shows great values in using melted nitrate to thermally decompose the epoxy resin of the printed circuit board. In the method, a printed circuit board (PCB) is dipped into the melted nitrate to thermally decompose the brominated epoxy resin in the PCB and to generate a great amount of organic gas and nitrogen oxide (NOx) through chemical reactions, as shown in FIG. 1. However, when a high concentration of organic gas happens to be mixed with oxygen (or air) in high temperature, there could be combustion (which could easily lead to fire and air blast) in the processing system; besides, when oxygen is introduced to incinerate the organic gas, extra energy is required to carry out the process; therefore, processing cost could increase. The factors affecting the processing efficiency in the pyrolysis process are listed as follows:
(1) The amount of gas generated by the pyrolysis process increases as the temperature rises, and it is difficult to control the amount of gas as the temperature goes even higher; which could pose a security threat to the operator.
(2) the used PCB will float on the processing fluid in the pyrolysis process; besides, when the PCB is horizontally inserted in the reactor, the glass fiber and the copper foil of the PCB will block the discharging path of the pyrolysis gas under the PCB and also make it difficult for the PCB to react in the pyrolysis process; therefore, when the operator tries to take out the processed PCB, a huge amount of gas will blow off and pose a security threat to the operator.
(3) In the pyrolysis process, if outside air comes in the reactor when the temperature is high, a fire or air blast could occur, the higher the temperature, the more likely it happens, which could pose a security threat to the operator.
(4) During the operation a lot of carbon residues will gather on the surface of the melted nitrate, the amount of the carbon residue is inversely proportional to the amount of gas, which is even more when the temperature is below 370° C.; since carbon only decomposes under very high temperature, and there's some gas hidden under the carbon residue, so the operator could encounter some risks when he/she tries to take out the carbon residue.
(5) When using oxygen to aerate the pyrolysis process, the added oxygen and the uncertainty of the amount of generated gas require more operating cost.
(6) Using blower to discharge the pyrolysis gas for oxygen aeration is not effective, meanwhile, the reactor could be in negative pressure to let outside air come in (which could lead to fire and air blast more easily); therefore, the system could be unstable and affect the operating efficiency.
(7) When the used PCB is inserted to/removed from the reactor in the pyrolysis process, outside air could come in the reactor and pose a huge risk; besides, the glass fiber on the used PCB could be damaged by the melted nitrate.
(8) Since the inlet of the reactor is disposed at a side of the reactor while the gas exhaust outlet is disposed on top thereof, a chimney effect could happen and let a huge amount of outside air come in the reactor, posing a great risk in operation.
Due to these phenomenons, it is necessary to propose a unique method for enhance the operating safety and the recycling efficiency when using the melted nitrate to thermally decompose the used PCB.
Therefore, the prior-art technique presents some shortcomings to be overcome.
In view of the deficiencies of the prior-art technique, after years of constant effort, the inventor has consequently invented and disclosed a method and a device using pyrolysis for recycling used printed circuit board in the present invention.